A conventional computer trackball uses an operating ball mechanically contacted with axles having wheels respectively to translate motions of the operating ball into signals on a coordinate of a cursor on a display of a computer.
Contamination on the surface of the operating ball from dirt or greasiness via the distal motion of a user, however, certainly will affect the moving of the cursor on the display abnormally. Therefore, the user has to clean the operating ball and connecting axles quite often. Not to mention about the surface being worn a bit.
It is known an optical trackball with speckles on the surface of the operating ball according to the U.S. Pat. No. 5,288,993, where the speckles have to be placed in a certain density, and also the color of the speckles has to contrast with the background color of the operating ball. Thus the cost to produce such an operating ball with speckles is quite high, and the procedure must be under precisely controlled when making the speckles upon the operating ball.